In a conventional cellular communication system, the coverage of a base station usually varies from 2 km to 5 km. If only the line-of-sight (LOS) transmission is adopted, due to the existence of tall buildings, shadow fading of the channels would be very apparent, and the quality and speed of the signals would be reduced. In the existing technology, an access point, such as a relay station, is installed, establishing between a mobile station and a base station an information channel having a high speed and a small fading, such that the communication quality is greatly improved. A relay station installed on a building or street is called a fixed relay station.
A mobile relay station (MRS) is a relay station installed on a movable carrier, for example, a transportation means (hereinafter referred to as a vehicle). When a user equipment (UE) is on the vehicle, the UE establishes a connection with a ground base station through the MRS, so as to solve the problem of coverage in the vehicle, and reduce the energy consumption of the UE. FIG. 1 is a schematic view of a communication system involving the MRS.
The cellular communication system of the existing technology as described above performs a handover of the UE from a serving cell to a target cell by using a “delay and margin” method.EPCCPCH—Ncell−EPCCPCH—Serving>Margin
“EPCCPCH—Ncell” EPCCPCH—Ncell−EPCCPCH—Serving in the equation represents a signal intensity of a primary common control physical channel (PCCPCH) of a target cell measured by the UE, “EPCCPCH—Serving” in the equation represents a signal intensity of a PCCPCH of a current serving cell measured by the UE, and Margin in the equation represents a handover margin.
When a time period T, within which the above equation EPCCPCH—Ncell>EPCCPCH—Serving+Margin is satisfied, and T is longer than a threshold value T0 (delay), the UE is handed over from the serving cell to the target cell.
Since the above handover process of the prior art is proposed for the conventional cellular network, it at least has the following problem. When a MRS starts to move from a static state, a relative movement may occur to a group of UEs accessing the MRS, and the UEs need to be handed over in time. However, due to the delay effect, the group of UEs may not be handed over in time.